The disclosure relates to a method for damping torsional vibrations, in particular in the drive train of energy generation installations, by means of closed-loop generator control and a device for implementing the method.
Drive trains comprising components such as gears, clutches and connecting elements (shafts), for example, are important parts of various electrical energy generation installations, such as, for example, wind energy installations, water power installations, etc.
The drive train performs the task of producing a mechanical connection between an input drive (for example a rotor of a wind energy installation) and an output drive (for example a corresponding generator), via which energy is transmitted by a rotary movement. Drive train components, such as gears, serve the purpose of converting the speed and the torque present at the input drive to values which correspond to the working range of the generator. If required, clutches are used for isolation between the input drive and the output drive and shafts produce the mechanical connection between the components involved. Other components, such as mechanical brakes or the like, can also be integrated in the drive train.
Since the components involved cannot be manufactured with any desired stiffness, but have a finite stiffness, they can be excited to produce natural vibrations. Such excitation can take place, for example, as a result of an input power which is not constant (in the case of wind energy installations, for example, as a result of gusts of wind or wind turbulences), as a result of external faults or as a result of self-motions of other installation components. Vibrations of a different origin can also result in vibrations in the drive train, in the case of a wind energy installation, for example, vibrations of the tower or vibrations as a result of meshing of a gear.
Vibrations have a disadvantageous effect on the life of the components involved, in particular the gear. Continuous pulsating loads increase the wear on the affected component parts and result in shorter replacement intervals, which has financial and technical implications for the installation and grid operator and reduces the installation's profits. In particular from the point of view of the predicted increase in the prevalence of wind energy installations in the offshore sector in the foreseeable future, this aspect will play an ever greater role since the replacement of damaged components will be even more difficult there. The aim is therefore to reduce these vibrations in order to extend the life of the components.
Although the present disclosure in the context of this application is described primarily with respect to wind energy installations, it is in no way restricted to wind energy installations or devices for energy generation, but can be used in principle in all devices in which torsional vibrations of shafts, spindles or the like, in particular also of shafts and spindles with interposed gears, can occur.
In order to avoid vibrations, it is known to configure the generator of an energy generation installation such that it can be adjusted by means of external actuating signals. In this case, the generator may be a double-fed asynchronous generator, for example, which is connected directly to the power supply system on the stator side and is supplied on the armature side via a DC voltage intermediate circuit, as a result of which voltages and currents of different frequencies and amplitudes can be impressed on the armature. Synchronous generators which are connected to the power supply system via converters with a DC intermediate circuit and are correspondingly adjustable are also used in the prior art. By virtue of the mentioned actuation possibilities, it is possible for the generator to be provided with a torque which is matched to the damage-causing vibrations, as a result of which it reduces these vibrations and correspondingly damps the torque present in the drive train.
Thus, DE 10 2007 019 907 B4 has disclosed a method which forms a control deviation on the basis of the generator speed via a vibrational delay element, from which a correction torque is determined for open-loop generator control.
A similar approach is pursued in US 2008/0067815, in accordance with which a signal is generated from changes in the generator speed, and this signal is used to realize damping via the generator actuating torque.
EP 1 507 331 A2 describes a method in which a generator actuating torque is generated from the generator speed specifically for synchronous generators.
Disadvantages with all of these solutions are considered to be the fact that the damage-causing vibrations of the torque are only determined with restricted accuracy and accordingly also the quality of the compensation operations is limited. In particular, the determination of the vibrations from the speed is subject to considerable inaccuracies.
By virtue of filtering the speed signal, this problem can be partially eliminated, but this increases the complexity in respect of damping and can result in further undesirable side effects, such as phase shifts of the signals.
U.S. Pat. No. 7,173,399 B2 has proposed, in this regard, measuring the torque via torque sensors and generating a corresponding actuating torque via load-commutated converters and current intermediate circuits. Instead of deriving an actuating torque from the speed, therefore, the torque itself is used directly, as a result of which the accuracy of the damping is improved. However, in this case the use of at least one further sensor is necessary in order to detect the torque to be damped. Therefore, the damping cannot be achieved on its own with the hardware already existing in an installation.
In the mentioned methods, there is the additional problem that vibrations are impressed on the torque present at the generator as a result of the compensation processes themselves, and these vibrations generally result in a correspondingly non-uniform electrical output power.
There is therefore a need for solutions which make it possible to continuously determine a torque, in particular in a drive train, on the basis of variables which are already determined, generally by means of existing hardware, and back-control (closed-loop) by means of adjusting a generator torque. In addition, there is a requirement for solutions for smoothing vibration-related fluctuations in the output power of such generators.